feat(python): add phrase query option for fts (#798)

addresses #797 

Problem: tantivy does not expose option to explicitly

Proposed solution here: 

1. Add a `.phrase_query()` option
2. Under the hood, LanceDB takes care of wrapping the input in quotes
and replace nested double quotes with single quotes

I've also filed an upstream issue, if they support phrase queries
natively then we can get rid of our manual custom processing here.

python/lancedb/query.py

@@ -468,6 +468,24 @@ class LanceFtsQueryBuilder(LanceQueryBuilder):
     def __init__(self, table: "lancedb.table.Table", query: str):
         super().__init__(table)
         self._query = query
+        self._phrase_query = False
+
+    def phrase_query(self, phrase_query: bool = True) -> LanceFtsQueryBuilder:
+        """Set whether to use phrase query.
+
+        Parameters
+        ----------
+        phrase_query: bool, default True
+            If True, then the query will be wrapped in quotes and
+            double quotes replaced by single quotes.
+
+        Returns
+        -------
+        LanceFtsQueryBuilder
+            The LanceFtsQueryBuilder object.
+        """
+        self._phrase_query = phrase_query
+        return self
 
     def to_arrow(self) -> pa.Table:
         try:
@@ -490,7 +508,11 @@ class LanceFtsQueryBuilder(LanceQueryBuilder):
         # open the index
         index = tantivy.Index.open(index_path)
         # get the scores and doc ids
-        row_ids, scores = search_index(index, self._query, self._limit)
+        query = self._query
+        if self._phrase_query:
+            query = query.replace('"', "'")
+            query = f'"{query}"'
+        row_ids, scores = search_index(index, query, self._limit)
         if len(row_ids) == 0:
             empty_schema = pa.schema([pa.field("score", pa.float32())])
             return pa.Table.from_pylist([], schema=empty_schema)

python/tests/test_fts.py

@@ -169,13 +169,16 @@ def test_syntax(table):
     table.create_fts_index("text")
     with pytest.raises(ValueError, match="Syntax Error"):
         table.search("they could have been dogs OR cats").limit(10).to_list()
+    table.search("they could have been dogs OR cats").phrase_query().limit(10).to_list()
     # this should work
     table.search('"they could have been dogs OR cats"').limit(10).to_list()
     # this should work too
     table.search('''"the cats OR dogs were not really 'pets' at all"''').limit(
         10
     ).to_list()
-    with pytest.raises(ValueError, match="Syntax Error"):
-        table.search('''"the cats OR dogs were not really "pets" at all"''').limit(
-            10
-        ).to_list()
+    table.search('the cats OR dogs were not really "pets" at all').phrase_query().limit(
+        10
+    ).to_list()
+    table.search('the cats OR dogs were not really "pets" at all').phrase_query().limit(
+        10
+    ).to_list()